1. Field of the Invention
The present invention relates to an Ethernet protection switching method, and more particularly to an Ethernet protection switching method based on a change in link status in an Ethernet link aggregation sublayer, wherein, when faults occur in an Ethernet link, the Ethernet link is protection-switched to an adequate link.
This work was supported by the IT R&D program of Ministry of Information and Communication (MIC)/Institute for Information Technology Advancement (IITA) [2005-S-102-03. Carrier Class Ethernet Technology].
2. Description of the Related Art
Ethernet protection switching may be performed in various manners, such as protection switching in a physical layer via detection of a fault at an optical link; transmission of information with an additional Ethernet frame through a protection link upon occurrence of a fault in an Ethernet link; simultaneous data transmission to dual links and use of one link selected from the dual links, and protection switching in a Physical Medium Dependent (PMD) layer.
However, adequately coping with faults caused by damage in other physical layers is difficult when employing protection switching in the PMD layer, and supporting protection switching of data flows above a Media Access Control (MAC) layer in the event of connection with a multi-stage system is difficult when protection switching is employed in some physical layers.
In Operation, Administration and Maintenance (OAM) in the MAC layer or layers above the MAC layer, i.e. in a MAC client domain, management relating to protection switching is performed based on connection to the MAC layer or layers above the MAC layer, particularly when performing the protection switching.
This connection originates and terminates at two flow end points, that is, Management Entity Group (MEG) end points. Ethernet link management and protection switching via a message to monitor a connection status between entities is necessary in an Ethernet network.
In monitoring the connection status for the Ethernet protection switching, continuity check messages between the MEG end points are observed to determine if they normally arrive at a preset frequency for a preset duration. Such a connection status monitoring scheme based on an exchange of the continuity check messages serves to manage and operate connections above the MAC layer without regard to the physical layer and multiple heterogeneous physical layers below the MAC layer.
In the case where a lower part of the physical layer is made of a single link or serially connected single-links, damage to the physical layer causes connections above the physical layer, i.e. exchange of the continuity check messages, to be interrupted. Hence, the Ethernet link management and protection switching may be performed through detection of problems in links and connections.
However, when an aggregation of links connected in parallel is used in some sections, the use of continuity check messages alone may fail to detect reduction of bandwidth due to failure of some links in the group, disrupting Ethernet traffic.
When a link-aggregated section, i.e. parallel connection, is present in a path that is formed by serially connected elements in the Ethernet links, the link aggregation sublayer resides between an Ethernet Client and the MAC layer (MAC Control layer) of the link aggregation sublayer, and the section is regarded as a single link in view of the layer above the MAC layer, i.e. Ethernet MAC Client.
In addition, when multiple Ethernet links are connected in parallel, multiple MAC addresses are present in actuality, but the layer above the MAC layer (i.e. Ethernet MAC Client) uses a single virtual logical MAC address of the link aggregation sublayer.
When all links in a link aggregation are simultaneously changed (by addition, deletion, or errors), the layer above the Ethernet MAC layer may treat the aggregated links as a single link. However, when some links in the link aggregation are changed (by addition, deletion, or errors), the layer above the Ethernet MAC layer should regard the change as variations in bandwidth and adjust the network connection structure. Therefore, an efficient method is needed for Ethernet link management and protection switching.
Further, when some links in the link aggregation have an error or are deleted, some others are still usable depending on a transmission scheme of the link aggregation sublayer and the continuity check messages may be transmitted between the MEG end points. In this case, reduced bandwidth leads to total failure of the Ethernet network. However, this trouble is not detected between the MEG end points and protection switching is not performed.